This research project is concerned with the isolation of different proteoglycans synthesized by endothelial cell cultures derived from rabbit aorta and with the study of their interaction with certain protein molecules of biological interest. Proteoglycans will be isolated by precipitation with lectins and their protein and polysaccharide moieties characterized. Particular attention will be devoted to heparin-like proteoglycans which are thought to bind te enzyme lipoprotein lipase at the endothelial cell surface. Antisera will be obtained against purified proteoglycans and used to characterize the structure of these compounds in vitro and to study the interaction enzyme-mucopolysacchaide at the cell surface.